Plunger rod comprising at least three annular elements for a prefilled syringe

ABSTRACT

A prefilled syringe includes a syringe body filled with a medical fluid, which has a nozzle at a front side, the nozzle being closed with a cap, and which is closed at a rear side with a displaceable plunger; and a plunger rod that can be inserted into the syringe body via the rear side. The plunger rod has a connecting portion at a front side, via whi9ch the plunger rod can be connected to the plunger. At least three annular elements, which extend at least in some sections about a longitudinal axis of the rod, are arranged on a rear side of the connecting portion on the plunger rod in such a manner that they are located in the syringe body when the plunger rod is fully connected to the plunger. The three annular elements support a coaxial connection of the rod to the plunger positioned in the syringe.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/555,220, filed Sep. 1, 2017, now U.S. Pat. No. 10,543,319, which is aU.S. national stage application of International Application no.PCT/EP2016/054351, filed Mar. 2, 2016, which claims the benefit of thefiling date of European Application No. 15000587.4, filed Mar. 2, 2015,the contents of which are hereby incorporated by reference in theirentirety.

The invention relates to a plunger rod for a syringe body prefilled witha medical fluid and to a syringe including the plunger rod and thesyringe body prefilled with the medical fluid.

WO 2014/053560 A1 discloses a syringe prefilled with a medical fluid. Inone embodiment, the plunger rod and the syringe body are mounted locatedside by side in an over pack. To use the syringe, the plunger rod andthe syringe body have first to be removed out of the over pack. Theplunger rod is then screwed into the plunger closing the rear end of thesyringe body. The content of the named patent application isincorporated fully into the present patent application by reference.

The object underlying the invention is to provide an improved plungerrod. The inserting, in particular the screwing, of the plunger rod intothe plunger is to be improved. In particular, leakage caused by tiltingthe plunger is to be avoided where possible. In addition, the guiding ofthe plunger rod in the syringe body is to be improved, in particularwhen using the syringe in a syringe pump.

Said object is achieved by the subject matter with the featuresaccording to the independent claims. Advantageous embodiments are theobject of the dependent claims, the description and the drawings.

The prefilled syringe according to the invention includes the followingcomponent parts: a syringe body which is filled with a medical fluid andcomprises on a front end a nozzle, which is closed by way of a cap, andwhich is closed on a rear end by way of a displaceable plunger, and aplunger rod which is insertable into the syringe body via the rear endand comprises on a front end a connecting portion, by means of which theplunger rod is connectable to the plunger, wherein at least threeannular elements, which extend at least in portions about a longitudinalaxis of the plunger rod, are arranged on the plunger rod on a rear endof the connecting portion such that when the plunger rod is fullyconnected to the plunger, they are situated in the syringe body. Thesyringe, in this case, is in its initial state. I.e. the plunger has notyet been moved to eject the fluid.

The three annular elements support a coaxial connection between theplunger rod and the plunger. The annular elements prove advantageous, onthe one hand, as they prevent tilting over the entire circumference of360°. On the other hand, the three annular elements make it possible forthe user, when connecting the plunger rod to the plunger, to have hapticand/or acoustic control. If, for example, the user connects the plungerrod correctly to the plunger immediately, he does not receive a hapticand/or acoustic message. If, for example, in contrast, the user tries,unintentionally, to connect the plunger rod incorrectly askew, he isable to perceive, in particular, the transition of the plunger rod fromthe central annular element to the rear annular element on the edge ofthe rear syringe body opening as a type of jump, preferably connected toa type of click. As a result, the user is able to recognize that he istrying to connect the plunger rod incorrectly to the plunger and canthen correct the position of the plunger rod in a corresponding manner.

The position of the plunger in the prefilled syringe body and theposition of the three annular elements on the plunger rod are matched toone another such that in a first step, when the plunger rod is placed byway of its connecting portion on the plunger, the two front rings arealready arranged in the interior of the syringe body. When connecting,for example screwing-in, the plunger rod is initially guided through thetwo front annular elements. The rear third ring supports the guiding ofthe plunger rod when the plunger rod is finally, fixedly connected tothe plunger.

The three annular elements are positioned in the interior of the syringebody no later than in the state in which the plunger rod is fullyconnected to the plunger, preferably is screwed into the plunger.

According to a first embodiment, an outside diameter of the threeannular elements is identical to an inside diameter of the syringe bodyor is somewhat smaller than an inside diameter of the syringe body. As aresult, the three annular elements can be guided on an inner side of thesyringe body when connecting the plunger rod to the plunger and laterwhen moving the plunger for ejecting the fluid. The outside diameter ofthe three annular elements is preferably identical.

In a further embodiment, wing elements or ribs, which extend radiallyoutwardly, are arranged distributed over the circumference of theplunger rods, preferably individually, between the annular elements. Thewing elements preferably connect the annular elements together. The wingelements are proved to be advantageous as they enable guidance in alonger, in portions continuous manner along the longitudinal axis of theplunger rod.

In one design, at least four wing elements are arranged preferably at anangle of 90° with respect to one another, in particular individually,between the annular elements. Guidance that is as coaxial as possible isto be supported as a result. The wing elements preferably comprise anoutside diameter which is identical to the inside diameter of thesyringe body or is somewhat smaller than the inside diameter of thesyringe body. In a first embodiment, the wing elements comprise adiameter which is identical to the outside diameter of the annularelements. The guidance of the plunger rod is improved even more as aresult. In a second embodiment, the wing elements comprise an outsidediameter which is smaller than an outside diameter of the annularelements. The haptic and/or acoustic control is improved as a resultwhen the plunger rod is connected to the plunger and/or when the plungerrod is inserted into the syringe body. In one design, the outsidediameter of the wing elements is reduced in relation to the outsidediameter of the annular elements by between 1 mm and 10 mm, preferablyby between 4 mm and 8 mm.

The prefilled syringe can be provided, for example, in an over pack. If,for example, the medical fluid is oxygen-sensitive and the syringe bodyis not sufficiently oxygen-impermeable, the syringe can be packaged inan oxygen-impermeable over pack, for example in a blister. The plungerrod can already be premounted, for example, on the plunger. However, itcan also not be premounted and be located next to the syringe body inthe over pack. Consequently, within the field of the invention is alsoan over pack having an interior in which the afore-described syringeaccording to the invention is enclosed.

In addition, within the field of the invention is also the plunger rod,in particular for a or for the aforementioned prefilled syringe. Theplunger rod includes a front-end connecting portion, by means of whichthe plunger rod is connectable to the plunger. In this case, at leastthree annular elements, which extend at least in portions about alongitudinal axis of the plunger rod, are arranged on a rear end of theconnecting portion. The three annular elements, preferably individually,are arranged at a distance R with respect to one another, where 0.5mm≤R≤20 mm, in a preferred manner 1 mm≤R≤10 mm and particularlypreferred 2 mm≤R≤8 mm. The annular elements have, for example, athickness of approximately between 0.5 mm and approximately 5 mm,preferably between approximately 1 mm and approximately 3 mm. Theplunger rod has a diameter D where 8 mm≤D≤30 mm and/or a length L where80 mm≤L≤150 mm.

In addition, a syringe is also claimed, including a syringe body, aplunger and the afore-described plunger rod, wherein the plunger ispositionable in the syringe body in such a manner and the three annularelements are arranged on the plunger rod in such a manner that, when theplunger rod is fully connected to the plunger, they are situated in thesyringe body. The syringe body is preferably prefilled with a medicalfluid.

The prefilled syringe can have, for example, a holding volume of between5 ml and 100 ml. The medical fluid can be or include, for example, afluid for enteral and/or parenteral nutrition and/or for infusion. Themedical fluid can be provided by a solution and/or by an emulsion. Themedical fluid can also include medical substances. According to oneembodiment, the medical fluid is or includes the medicinal fluidPropofol, in particular a Propofol emulsion. Propofol is described bythe chemical name 2,6-diisopropylphenol (IUPAC).

The syringe body can be molded from plastics material, which includesone of the following polymers: cyclo-olefin copolymer, cyclo-olefinpolymer or crystal clear polymer. Such a plastics material container isresistant to solvents. In particular, such a plastics material containercan be used to store Propofol which acts as a solvent. The outer sidesof the plunger and/or the inner side of the syringe body are preferablycoated at least in portions with a lubricant, preferably aresiliconized.

According to one embodiment, the plastics material plunger rod is moldedfrom plastics material which preferably includes one of the followingpolymers: cyclo-olefin copolymer, cyclo-olefin polymer or crystal clearpolymer, or it is molded from polypropylene.

The invention is described in detail below by way of exemplaryembodiments in connection with the drawings, in which:

FIG. 1 .a shows a side view of a plunger rod according to a firstembodiment of the invention;

FIG. 1 .b shows a side view of a prefilled syringe according to theinvention with the plunger rod from FIG. 1 .a;

FIG. 2 .a shows a side view of a plunger rod according to a secondembodiment of the invention;

FIG. 2 .b shows a side view of a prefilled syringe according to theinvention with the plunger rod from FIG. 2 .a;

FIG. 2 .c shows a perspective view of the plunger rod according to thesecond embodiment of the invention from FIG. 2 .a;

FIG. 3 shows a perspective view of a plunger rod according to a thirdembodiment of the invention and

FIG. 4 shows a perspective view of a plunger rod according to a fourthembodiment of the invention.

FIG. 1 .a shows a plunger rod 15′ according to a first embodiment of theinvention. The plunger rod 15′ has a substantially cross-shaped crosssection and is formed by the two legs 3. Stabilizing elements 7 aremounted along the longitudinal axis. The rear end of the plunger rod 15′is closed off by a flange 4 with a larger diameter. The notches 5provided on the rear end enable the plunger rod 15′ (as a component partof the syringe 20) to be operated in a syringe pump. The plunger rod 15′is designed for operation in a syringe 20 with a holding volume ofbetween approximately 50 ml and 70 ml. A graduation 6 to 50 ml isprovided on the plunger rod 15′. The plunger rod 15′ has a diameter Dwhere 25 mm≤D≤30 mm and/or a length L where 100 mm≤L≤150 mm.

The front end of the plunger rod 15′ is provided by a connecting portion1, by means of which the plunger rod 15′ is connected to a plunger 12,not shown here, (see FIG. 1 .b in this respect). The connecting portion1 is provided here, as an example, by a screw thread. Three annularelements 2 a, 2 b, 2 c connect to the rear end of the connecting portion1. As a result, when the plunger rod 15″ is screwed into the plunger 12,it is possible, in particular, for the user to have haptic and/oracoustic control. The annular elements 2 a, 2 b, 2 c preferably extendover the entire circumference of the plunger 15′. The front annularelement 2 a additionally forms the stop when the plunger rod 15′ isscrewed into the plunger 12. The three annular elements 2 a, 2 b, 2 care preferably arranged equidistantly with respect to one another. Inone embodiment, the three annular elements 2 a, 2 b, 2 c are arrangedindividually at a distance R of between 2 mm and 8 mm with respect toone another. The annular elements 2 a, 2 b, 2 c have for example, athickness of approximately between 0.5 mm and approximately 5 mm,preferably of approximately between 1 mm and approximately 3 mm.

The cross-shaped cross section of the plunger rod 15′ is also continuedbetween the three annular elements 2 a, 2 b, 2 c. Ignoring the flange 4and the connecting portion 1, the diameter D of the plunger rod isidentical or substantially identical along the longitudinal axis. As aresult, so-called wing elements 3 a, 3 b or ribs are formed between thethree annular elements 2 a, 2 b, 2 c. The front, here four, wingelements 3 a connect the front ring 2 a to the central ring 2 b. Therear, here four, wing elements 3 b connect the central ring 2 b to therear ring 2 b. The annular elements 2 a, 2 b, 2 c and the wing elements3 a, 3 b enable the plunger rod 15′ to be guided into the syringe body 8in as coaxial a manner as possible and, as a result, enable the plungerrod 15′ to be screwed into the plunger 12 in as coaxial a manner aspossible (see FIG. 1 .b in this respect). Placing the plunger rod 15′ onthe plunger 12 at an angle, leading to possible tilting of the plunger12 and finally possibly to resultant leakage can be reduced or evenavoided as a result.

FIG. 1 .b illustrates the use of the plunger rod 15′ from FIG. 1 .a in aprefilled syringe 20. The syringe 20 includes a syringe body 8 with anozzle 9 arranged on the front end of the syringe body 8, a cap 11closing the nozzle 9, a plunger 12 which is arranged in the syringe body8 and closes the interior of the syringe body 8 in a fluid-tight manner,and the plunger rod 15′ from FIG. 1 a which is connected to the plunger12 by means of its connecting portion 1. The connection between theplunger 12 and the plunger rod 15′ is provided here by means of a screwconnection. A thread, which is, however, not shown in the figure, isalso provided in a corresponding manner in the interior of the plunger12.

The outside diameter D or D_(F) of the plunger rod 15′ and/or of theannular elements 2 a, 2 b, 2 c and/or of the wing elements 3 a, 3 b canbe identical to the inside diameter of the syringe body 8. In order tomake it easier for the plunger rod 15′ to move in the syringe body 8,the outside diameter D or D_(F) of the plunger rod 15′ and/or of theannular elements 2 a, 2 b, 2 c and/or of the wing elements 3 a, 3 b is,in particular, smaller than the inside diameter of the syringe body 8.The outside diameter D or D_(F) is preferably reduced in relation to theinside diameter of the syringe body 8 by approximately between 0.5 mmand 5 mm.

The prefilled syringe 20 can be filled, for example, via its initiallyopen rear end and then can be closed by way of the plunger 12. Theplunger rod 15′ can then be connected to the plunger 12 at a later pointin time, for example shortly before the application. However, theplunger 12 can also, for example, be inserted into the syringe body 8with the plunger rod 15′ already screwed into the plunger 12.

The position of the plunger 12 in the prefilled syringe body 8 and theposition of the three annular elements 2 a, 2 b, 2 c on the plunger rod15′ are preferably matched to one another in such a manner that in afirst step, when the plunger rod 15′ is placed on the plunger 12 by wayof its connecting portion 1, the two front rings 2 a, 2 b are alreadyarranged in the interior of the syringe body 8 and are preferably guidedby the inner side of the syringe body 8. When being screwed in, theplunger rod 15′ is initially guided by the two front annular elements 2a, 2 b and the front wing elements 3 a and then also by the rear wingelements 3 b in the syringe body 8. The rear third ring 2 c supports theguiding of the plunger rod 15′ in the final, fixed connection betweenthe plunger rod 15′ and the plunger 12. The three rings 2 a, 2 b, 2 care positioned in the interior of the syringe body 8 no later than inthe state in which the plunger rod 15′ is fully connected to the plunger12, preferably is screwed into the plunger 12. The annular elements 2 a,2 b, 2 c prove to be advantageous as they prevent tilting over theentire circumference of 360°. The wing elements 3 a, 3 b prove to beadvantageous as they enable longer guidance along the longitudinal axisof the plunger rod 15′. The present invention joins said advantagestogether.

FIGS. 2 .a to 2.c show a plunger rod 15″ according to a secondembodiment of the invention. Only the differences to the plunger rod 15′from FIG. 1 .a are explained below. For all the other components,reference is made to the preceding description concerning FIG. 1 .a. Theplunger rod 15″ does not have a graduation. In contrast to theembodiment shown in FIG. 1 .a, the wing elements 3 a, 3 b, which connectthe three annular elements 2 a, 2 b, 2 c together, do not have theidentical outside diameter as the three annular elements 2 a, 2 b, 2 c.The outside diameter D_(F) of the wing elements 3 a, 3 b is smaller thanthe outside diameter D of the three annular elements 2 a, 2 b, 2 c. Theoutside diameter D_(F) of the wing elements 3 a, 3 b is preferablyreduced by approximately between 4 mm and 8 mm in relation to theoutside diameter D of the annular elements 2 a, 2 b, 2 c. In the presentcase, there are precisely three annular elements which are located inthe front region of the plunger rod 15′.

As a result, when screwing the plunger rod 15″ into the plunger 12, itis possible, in particular, for the user to have haptic and/or acousticcontrol. If the user screws the plunger rod 15″ correctly into theplunger 12 immediately, he does not receive a haptic and/or acousticmessage. If, in contrast, the user tries, unintentionally, to screw theplunger rod 15″ into the plunger 12 incorrectly askew, he is able toperceive, in particular, the transition of the plunger rod 15″ from thecentral annular element 2 b to the rear annular element 2 c on the edge14 in the rear syringe body opening (see FIG. 2 .b in this respect) as atype of jump, preferably connected to a type of click. As a result, theuser is able to recognize that he is trying to connect the plunger rod15″ incorrectly to the plunger 12 and then he can correct the positionof the plunger rod 15″ in a corresponding manner.

In addition, FIG. 3 shows a plunger rod 15′″ according to a thirdembodiment of the invention. The design of said plunger rod 15′″corresponds substantially to the design of the plunger rod 15″ fromFIGS. 2 .a to 2.c. The present plunger rod 15′″ simply comprisesdifferent dimensions as it is designed for a syringe 20 with a holdingvolume of between approximately 20 ml and 30 ml. The plunger rod 15′″has a diameter D where 13 mm≤D≤23 mm and/or a length L where 100mm≤L≤150 mm. The distance R between the annular elements here is also 2mm≤R≤8 mm.

Finally, FIG. 4 shows a plunger rod 15″″ according to a fourthembodiment of the invention. The design of said plunger rod 15″″corresponds substantially to the design of the plunger rods 15″ and 15′″from FIGS. 2 .a to 2.c and 3. The present plunger rod 15″″ simplycomprises different dimensions as it is designed for a syringe 20 with aholding volume of between approximately 10 ml and 15 ml. The plunger rod15″″ has a diameter D where 8 mm≤D≤18 mm and/or a length L where 80mm≤L≤110 mm. The distance R between the annular elements here is 2mm≤R≤8 mm. In addition, no stabilizing elements 7 are provided on theplunger rod 15′″.

It is clear to the person skilled in the art that the describedembodiments are to be understood as examples. The invention is notlimited to said embodiments but can be varied in many different wayswithout departing from the essence of the invention. Features ofindividual embodiments and the features named in the general part of thedescription can be combined with one another both individually andtogether.

The invention claimed is:
 1. A prefilled syringe comprising a syringebody which is filled with a medical fluid and comprises, on a front endthereof, a nozzle, which is closed by way of a cap, wherein the syringebody is closed, on a rear end thereof, by way of a displaceable plunger,and a plunger rod, which is insertable into the syringe body via therear end of the syringe body and comprises, on a front end thereof, aconnecting portion by means of which the plunger rod is connectable tothe plunger, wherein at least three annular elements extend along aportion of a longitudinal axis of the plunger rod, the portion beingnext to a rear end of the connecting portion, wherein the portionextends from a proximal-most annular element to a distal-most annularelement, wherein, when the connecting portion of the plunger rod isfully connected to the plunger, the at least three annular elements aresituated in the syringe body, wherein the annular elements engage thesyringe body to promote maintenance of a coaxial position of the plungerrod relative to the plunger while the connecting portion is beingconnected to the plunger, wherein wing elements, extend radiallyoutwardly and connect the at least three annular elements together, thewing elements being distributed along a circumference of the plungerrod, wherein an outside diameter (D_(F)) of the wing elements within theportion along which the three annular elements extend is smaller than anoutside diameter (D) of the at least three annular elements, and whereinthe rear end of the plunger rod is closed off by a flange.
 2. Theprefilled syringe as claimed in claim 1, wherein a position of theplunger in the prefilled syringe body and the position of the at leastthree annular elements on the plunger rod are matched to one anothersuch that in a first step, when the plunger rod is placed by way of itsconnecting portion on the plunger, two of the at least three annularelements are arranged in the interior of the syringe body.
 3. Theprefilled syringe as claimed in claim 2, wherein the outside diameter(D) of the at least three annular elements and an inside diameter of thesyringe body are selected to enable the at least three annular elementsto engage the syringe body.
 4. The prefilled syringe as claimed in claim2, wherein the outside diameter (D) of the at least three annularelements is identical.
 5. The prefilled syringe as claimed in claim 2,wherein at least four wing elements are arranged to form anglestherebetween, each angle being 90°, wherein the at least four of thewing elements are arranged between two of the at least three annularelements.
 6. The prefilled syringe as claimed in claim 1, wherein theoutside diameter (D) of the at least three annular elements and aninside diameter of the syringe body are selected to enable the at leastthree annular elements to engage the syringe body to permit guiding theplunger rod in the syringe body.
 7. The prefilled syringe as claimed inclaim 1, wherein the outside diameter (D) of the at least three annularelements is identical.
 8. The prefilled syringe as claimed in claim 1,wherein at least four of the wing elements are arranged, to form anglestherebetween, each angle being 90°, wherein the at least four of thewing elements are arranged between two of the at least three annularelements.
 9. The prefilled syringe as claimed in claim 1, wherein theoutside diameter (D_(F)) of the wing elements is selected to enable thewing elements to engage the syringe body.
 10. The prefilled syringe asclaimed in claim 1, wherein the outside diameter (D_(F)) of the wingelements is substantially the same as the outside diameter (D) of the atleast three annular elements.
 11. The prefilled syringe as claimed inclaim 1, wherein the outside diameter (D_(F)) of the wing elements isless than the outside diameter (D) of the at least three annularelements by between 1 mm and 10 mm.
 12. The prefilled syringe as claimedin claim 1, wherein the plunger rod is premounted on the plunger. 13.The prefilled syringe as claimed in claim 1, wherein the plunger rod islocated next to the syringe body in an oxygen-impermeable, over pack.14. An oxygen-impermeable over pack having an interior in which thesyringe as claimed in claim 1, wherein it is hermetically enclosed. 15.A plunger rod for a prefilled syringe as claimed in claim 1, including afront-end connecting portion, the plunger rod being connectable to aplunger, wherein the at least three annular elements, extend at least inportions about a longitudinal axis of the plunger rod and are arrangedat a distance R, wherein 0.5 mm≤R≤20 mm.
 16. A pre-filled syringe asclaimed in claim 1, the pre-filled syringe including a plungerpositionable in the syringe body and the at least three annular elementsare arranged on the plunger rod such that, when the plunger rod is fullyconnected to the plunger, the at least three annular elements aresituated in the syringe body.
 17. The prefilled syringe as claimed inclaim 1, wherein the wing elements are individually arranged between theat least three annular elements.
 18. The prefilled syringe as claimed inclaim 1, wherein the outside diameter (D_(F)) of the wing elements isless than the outside diameter (D) of the at least three annularelements by between 4 mm and 8 mm.
 19. A plunger rod for a prefilledsyringe as claimed claim 1, including a front-end connecting portion,the plunger rod being connectable to a plunger, wherein the at leastthree annular elements extend at least in portions about a longitudinalaxis of the plunger rod and are arranged at a distance R, wherein 1mm≤R≤10 mm.
 20. An oxygen-impermeable overpack comprising: a prefilledsyringe and a plunger rod; wherein the prefilled syringe and the plungerrod are hermetically enclosed within an interior of the oxygenimpermeable overpack; the plunger rod including a front-end connectingportion by means of which the plunger rod is connectable to a plunger,wherein at least three annular elements which extend at least inportions about a longitudinal axis of the plunger rod and which arearranged on a rear end of the connecting portion at a distance R,wherein 0.5 mm≤R≤20 mm, wherein wing elements, extend radially outwardlyand connect the at least three annular elements together, the wingelements being arranged distributed over a circumference of the plungerrod, an outside diameter (D_(F)) of the wing elements is smaller than anoutside diameter (D) of the at least three annular elements, wherein therear end of the plunger rod is closed off by a flange.
 21. A plunger rodfor a prefilled syringe, the plunger rod comprising a front endconnecting portion, by means of which the plunger rod is connectable toa plunger, wherein at least three annular elements which extend at leastin portions about a longitudinal axis of the plunger rod and which arearranged on a rear end of the connecting portion at a distance R,wherein 0.5 mm≤R≤20 mm, wherein wing elements, extend radially outwardlyand connect the at least three annular elements together, the wingelements being arranged distributed over a circumference of the plungerrod, an outside diameter (D_(F)) of the wing elements is smaller than anoutside diameter (D) of the at least three annular elements, wherein therear end of the plunger rod is closed off by a flange.
 22. A prefilledsyringe comprising a syringe body having a front end and a rear end,said syringe body being filled with a medical fluid, a displaceableplunger that closes said body at said rear end, a nozzle at said frontend, a cap that closes said nozzle, and a plunger rod that is insertableinto said syringe body at said rear end thereof, wherein said plungerrod that extends along a longitudinal axis, said plunger rod comprisingwing elements distributed along a circumference of said plunger rod andextending radially outward from said longitudinal axis, a connectingportion that is configured to connect to said displaceable plunger atsaid rear end, and three annular elements that extend along a portion ofsaid longitudinal axis, said portion being next to a rear end of saidconnecting portion, said portion extending from a proximal-most annularelement to a distal-most annular element, said three annular elementsbeing connected to each other by said wing elements, wherein, when saidconnecting portion of said plunger rod is fully connected to saiddisplaceable plunger, said three annular elements are situated in saidsyringe body, wherein the annular elements engage the syringe body topromote maintenance of a coaxial position of the plunger rod relative tothe plunger while the connecting portion is being screwed into theplunger, wherein an outside diameter of the wing elements within theportion along which the three annular elements extend is smaller than anoutside diameter of the at least three annular elements, and wherein therear end of the plunger rod is closed off by a flange.